JPS6353130B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for changing the shape of spinel-based particles.

According to the method of the present invention, particles with spherical and angular shapes can be produced in large quantities without using special granulation means, so the production cost is lower than when producing these particles by other methods. It becomes possible to lower it to a wide width.

Spinel is a complex oxide that has been known for a long time, and despite its many excellent properties, its uses have not been sufficiently developed compared to other oxides such as alumina and magnesia. A major reason why the development of applications for spinel has been delayed compared to other oxides is that spinel does not exist naturally enough to be used as an industrial resource.
We have no choice but to rely on artificially synthesized materials, but in this case, the cost of synthesizing spinel is extra compared to simple oxides such as alumina and magnesia. It has few outstanding properties that cannot be replaced by simple oxides such as these.

In view of this situation, the present inventors searched for a method of manufacturing and using spinel at low cost. As a result, the present inventors found that spinel can be produced successfully without the granulation process that is required when conventionally using spinel. They discovered a method of obtaining inexpensive granules and came up with the present invention.

Traditionally, when using spinel, its chemical composition, shape, and physical properties must be compatible with its intended use. For example, when spinel is used as a catalyst carrier, it must be highly pure, spherical, and have a large porosity with low bulk density; when used as particles for refractories,
These particles are of high purity and have a large bulk specific gravity, and as for the shape, angular ones are better in some cases, while spherical ones are better in others, and when used for grinding in a ball mill etc. This includes the fact that they are large particles. Conventionally, in order to provide shapes suitable for the above-mentioned uses, methods have been used in which synthesized spinel powder is granulated, or a composition that becomes spinel when fired is granulated and fired.
Powder granulation requires considerable equipment and is lost during these steps when the powder is brought down to a suitable temperature for granulation or when water is added to facilitate granulation. The amount of thermal energy is also not trivial.

The present invention does not require a special granulation process and can easily produce particles with both spherical and angular shapes. Therefore, it is not only possible to produce spinel particles that are suitable for all of the above-mentioned uses. This makes it possible to use spinel for uses other than those mentioned above.

The present invention combines magnesium hydroxide and/or magnesium oxide with aluminum hydroxide and/or aluminum oxide, and
The total of MgO 20-70% by weight, Al ₂ O ₃ 80-30% by weight, and other components is adjusted to 2% by weight or less, and the prepared raw material is heated to a cake containing water at a maximum temperature of 1300 %. This is a method for producing a granulated product containing spinel as a main component, which is characterized by firing in a rotary kiln at a temperature of ℃ or higher.

Spinel has a molar composition ratio of MgO and Al ₂ O ₃ of 1:1.
(MgO28.3:Al ₂ O ₃ 71.7 in weight ratio), but the spinel raw material actually used is MgO,
The blending ratio of Al ₂ O ₃ is selected depending on the purpose. However, if this blending ratio is too drastically changed to one with more MgO, the properties of magnesia become more pronounced than those of spinel, and conversely, if this blending ratio is too drastically changed to one with more Al ₂ O ₃ The properties of alumina become more pronounced than those of spinel. Here, as a result of searching for a blending ratio of MgO and Al ₂ O ₃ that can fully utilize the properties as spinel, we found that MgO is 20 to 70% by weight, Al ₂ O ₃ 80%
It was found that the range of ~30% by weight sufficiently exhibits the properties as a spinel as a whole, and the shape of the granulated product is easily controlled. In order to synthesize and sinter spinel, components other than MgO and Al ₂ O ₃ sometimes have a large effect. For this reason, it has been recognized that it is more convenient to control the shape of the spinel-based particles and various physical properties if the amount of components other than MgO and Al ₂ O ₃ is as small as possible. MgO _{, Al2O3}
It is recognized that if the amount of other components is 2% by weight or less, the effect will be small, and if it is 1% by weight or less, the effect will be even less, which is convenient for controlling the shape of the particles and various physical properties. Ta.

Spinel MgO and Al ₂ O ₃ used in the present invention
Although the use of natural raw materials is not specifically excluded, artificial raw materials such as seawater magnesia and Bayer process alumina are usually used because they are easy to obtain raw materials of consistent quality and high purity. Since these raw materials are obtained as fine powder products, they do not require any special treatment such as pulverization, but it is necessary to select a particle size depending on the purpose. Particularly when the purpose is to obtain a sintered body with higher density, it is desirable to use particles as fine as possible, preferably particles in which most of the particles are 15 μm or less in size.
Magnesia raw material (magnesium hydroxide or magnesium oxide) and alumina raw material (aluminum hydroxide or aluminum oxide) used in the present invention
The combination is determined depending on the purpose.

The blended raw materials are prepared into a cake by adding water if necessary. The amount of water contained in this cake-like blended raw material varies depending on the properties of the raw material particles used, but is usually in the range of 40 to 25% by weight. Another excellent method is to knead aluminum hydroxide or magnesium oxide powder into a cake of magnesium hydroxide obtained in the process of manufacturing seawater magnesia. This cake-like mixed raw material is put into a rotary kiln, where it is granulated, and spinel synthesis and sintering are performed in the rotary kiln.

There is a close relationship between the length of the rotary kiln, the circumferential speed of the rotary kiln, and the shape of the particles.The longer the length of the rotary kiln and the faster the circumferential speed, the rounder the particles will be. To produce angular particles of
It is preferable that the length of the rotary kiln is 30 m or less and the circumferential speed is 1 m/min or less. In order to obtain particles close to spheres, the length of the rotary kiln is 30 m or more and the circumferential speed is 3 m/min or more. Preferably, the speed is more preferably 5 m/min or more.

If the temperature at which the particles are fired is lower than 1300°C, there will be a large amount of unreacted materials, and if the temperature is higher than 1300°C, most of the spinel formation will be completed. The firing temperature of the particles varies depending on the intended use of the particles, with temperatures close to 1,300°C when using active surfaces such as catalyst supports, and temperatures of 1,700°C or higher when clinker is used for refractories. This is desirable.

Hereinafter, the effects of the present invention will be explained with reference to Examples.

Example 1 Moisture content obtained from the manufacturing process of seawater magnesia
A 48.6% by weight magnesium hydroxide cake and fine particles of aluminum hydroxide obtained by the Bayer method were kneaded while adding water to obtain a raw material cake with a water content of 35% by weight. This cake was fed to a rotary kiln with a circumferential speed of 0.5 m/min and a length of 7 m, and fired at temperatures of 1500°C and 1900°C. The chemical analysis value of the fired product is
MgO35.4%, _{Al2O3 63.5} %, CaO0.4%, _{Fe2O3 0.1}
%, SiO ₂ 0.2%, and the bulk specific gravity of the product fired at 1500℃ is
1.4, and the bulk specific gravity of the product fired at 1900°C was 3.01. The shape of the product fired at 1500℃ is shown in the micrograph in Figure 1.
The micrograph in the figure shows the shape of the particles fired at 1900°C. As seen in the photograph, the shape of the obtained particles was angular.

Example 2 Moisture content obtained in the manufacturing process of seawater magnesia
A 48.6% by weight magnesium hydroxide cake and fine aluminum oxide obtained by the Bayer method were kneaded while adding water to obtain a raw material cake with a water content of 32% by weight. This cake was fed to a rotary kiln with a peripheral speed of 4 m/min and a length of 40 m, and baked at a temperature of 1700°C. Chemical analysis values of the fired product are MgO 59.2%, Al ₂ O ₃ 40.0%,
The content was 0.5% CaO, 0.1% Fe ₂ O ₃ and 0.2% SiO ₂ , and the bulk specific gravity was 2.98. The shape of the particles of the fired product is shown in the micrograph of FIG. 3, and as shown in this photo, most of the obtained particles were rounded and almost spherical.

Example 3 Magnesium oxide powder obtained in the process of manufacturing seawater magnesia and aluminum oxide powder obtained by the Bayer method were mixed and ground in a dry process using a pulverizer, and water was added to the obtained pulverized mixture to give a water content of 37. % cake, and this cake was set at a circumferential speed of 5 m/
The material was then fed into a 40 m long rotary kiln and fired at a temperature of 1800°C. Chemical analysis values of the fired product are MgO49.7%,
Al ₂ O ₃ 49.2%, CaO 0.4%, Fe ₂ O ₃ 0.3%, SiO ₂ 0.2%
The bulk specific gravity was 3.10. The shape of the fired product is shown in the micrograph of FIG. 4, and as shown in this photograph, most of the obtained particles were rounded and almost spherical.

[Brief explanation of drawings]

FIG. 1, FIG. 2, FIG. 3, and FIG. 4 each show microscopic photographs of particles obtained in Examples of the present invention.

Claims (1)

[Claims] 1 Blend magnesium hydroxide and/or magnesium oxide with aluminum hydroxide and/or aluminum oxide, and the total amount of MgO 20 to 70% by weight, Al ₂ O ₃ 80 to 30% by weight, and other components is 2 in terms of fired product. % by weight or less, and put the prepared raw material in the form of a cake containing water without molding it in a rotary kiln with a maximum temperature of 1300°C or higher, adjusting the length and rotational speed of the kiln. 1. A method for producing granules containing spinel as a main component, characterized by obtaining granules of arbitrary shapes, such as spherical or angular shapes, by controlled firing.